bugfix/current-deprecated Return type of ClickHouseDB\Statement::current() should either be compatible with Iterator::current()

Author: m1khal3v

src/Statement.php

@@ -578,6 +578,9 @@ public function rewind(): void {
         $this->iterator = 0;
     }
 
+    /**
+     * @return mixed
+     */
     public function current() {
         if (!isset($this->array_data[$this->iterator])) {
             return null;